Power distribution systems may include technology to provide circuit protection, fault isolation, circuit reconfiguration (typically for restoration of service to stranded, load-side customers) and system return-to-normal functions. For example, the power distribution system may include fault protection devices including: source protection devices, such as circuit breakers, load protection devices, such as fuses, and fault protection devices, such as fault interrupters, sectionalizers, reclosers and the like, that segment a distribution line and permit fault isolation. While various strategies may be employed to manage the power distribution system to maintain service and to protect the power distribution system, typically the fault protection devices should operate in a coordinated manner to optimize performance of the power distribution system and to minimize the scope and duration of service interruptions. That is, to isolate a fault at the fault protection device nearest the fault to protect the source and to preserve service to loads between the source and the fault protection device.
At the same time, the power distribution system should be manageable, recoverable and operable at a high level of performance with reduced burden. These goals become difficult to obtain as the distribution system becomes heavily populated with fault protection devices.
Wide area communication systems have been employed for several decades as a means to enhance the automation of electric power distribution systems to provide management and system recovery. These systems are responsible for controlling the distribution of power from sources/substations out over medium voltage feeders/distribution lines to consumers and are typically radio based due to the high cost of providing fiber or other fixed communication media over a wide geographic area. An example of commercial communication products include the Utilinet radio, sold by Schlumberger, Inc. Most of these products are used in conjunction with SCADA systems, or other low to medium-speed communication applications such as the IntelliTEAM® circuit reconfiguration system, available from S&C Electric Company, Chicago, Ill.
Circuit/equipment protection systems, on the other hand, require high speed (low latency) and high reliability communications. Some of these systems are or can also be radio-based. An example of such a system includes the HRDS system available from S&C Electric Company. These systems utilize dedicated point-to-point links and dedicated communication channels for each pair of communicating devices. A company called Freewave Communications offers a radio-based off-the-shelf product for use in conjunction with the Schweitzer Engineering Laboratories, Inc. (SEL) mirrored-bits communication protocol. With these two technologies, digital status points can be conveyed between two interconnected distribution automation control devices over radio-based communication infrastructure.
There are a number of drawbacks to these radio-based, dedicated point-to-point systems:
1) Each point-to-point link requires dedicated infrastructure including dedicated channels and often dedicated radio pairs and repeaters. This makes the cost prohibitive and the installation and maintenance process cumbersome.
2) In grid-style power distribution topologies, it may take many of these point-to-point links to provide comprehensive coordination of protective devices.
3) If the communication path fails, it is difficult (and in many systems impossible) to create an alternative communication path “on-the-fly” to restore the communication between end devices.
4) The paths cannot be used as general purpose, routable communication paths to exchange other communication traffic because this could compromise the low-latency message delivery requirements of protection applications.
Mesh-topology communication systems or communication systems based upon the Internet's Ad-Hoc Routing methodology and spread-spectrum radios address several of the foregoing concerns, but not all. Bandwidth and/or latency-related issues remain, particularly when the systems are allowed to carry other competing communication traffic.
The apparent bandwidth solution is to simply increase the BAUD rate of the radios relative to the volume of communication traffic until adequate latency performance can be assured. However, a limitation is rapidly reached, as the effective range of all of the radio devices decreases with increasing BAUD rate. Increasing the number of intermediate devices in this situation only worsens the latency performance and increases maintenance concerns. Adding additional channels can also reduce the latency of the communication traffic, but this requires additional hardware, which may prove cost prohibitive.
What is needed is a communication system that can respond quickly and efficiently to prioritized or emergency communication traffic. Such a system may respond to more than one priority of message traffic, and may do so without loosing lower priority traffic. A communication device in this system may also recognize the presence of prioritized or emergency traffic even if the device is not an active participant in the communication exchange, responding by reducing its own burden on the system. The communication system may also support complex interconnectivity and alternate communication paths to provide consistent, reliable high speed radio-based communication. The system should do so without requiring complex, time-consuming configuration.